News release

From: Springer Nature

Drought may promote antibiotic resistance in soil microbes

Drought conditions can increase the concentration of natural antibiotics in soil and promote the growth of antibiotic-resistant bacteria, according to research published in Nature Microbiology. Using clinical data from 116 countries, the authors also report an association between local dryness levels and the average frequency of antibiotic resistance in hospitals, suggesting another way climate change may affect public health.

Soils are a rich source of natural antibiotic compounds, and many soil microbes have evolved mechanisms to survive exposure to them. However, it is unclear how more frequent and prolonged droughts driven by climate change may affect the balance of antibiotic-producing and antibiotic-resistant microbes in soil. It is also not certain whether this will have any implications for human health.

Dianne Newman, Xiaoyu Shan and colleagues combined computational analyses with laboratory experiments to examine how drying affects soil antibiotic dynamics. They compiled five metagenomic datasets from previous studies, including soils from cropland and grassland in California, USA; forest in Valais, Switzerland; and wetland in Nanchang, China. The authors then assessed how the quantities of microbial antibiotic-producing and antibiotic-resistance genes changed based on soil dryness. They found that the abundance of antibiotic-producing genes significantly increased under drought conditions in all five datasets, including for β-lactam antibiotics (such as penicillin) and macrolide antibiotic classes. In laboratory experiments using representative soil samples, under drought conditions, antibiotic levels became more concentrated and there was a 99% reduction in the relative fitness of some antibiotic-sensitive bacteria strains. However, antibiotic-resistant bacteria — including Gram-negative strains — showed no reduction in relative fitness.

When comparing antibiotic resistance data from hospitals in 116 countries to local annual precipitation and mean temperature, the authors found that greater aridity is associated with a higher average frequency of antibiotic resistance among clinical isolates. Although they note that further research is needed to demonstrate causality, these findings suggest that the risk posed by antibiotic resistance may be heightened by increased soil dryness driven by climate change.